You don’t really get LORs from well known (or famous) advisors as an undergrad at a major research University…after getting a PhD, the thought of this is kinda absurd. My PhD advisor was at least well known. I liked him, and he was a genuinely decent guy. However, he had a huge lab where grad students managed the undergrads, senior grad students or post-docs managed the junior grad students, research faculty managed the post-docs and senior grad students, and the well known advisor didn’t really manage anything. He literally did not know the names of the undergrads working for him sometimes. The post-docs and research faculty wrote the letters for the undergrads.